A nosocomial infection is an illness acquired as a result of healthcare, caused by an infectious agent that was not present or incubating at the time of hospital admission. Greater than 2.1 million nosocomial infections occur in the US annually. Most studies of nosocomial infections have been performed in adults; these studies have not examined risk factors unique to children. Children have differences in developmental immunity, which may make them more susceptible than adults to nosocomial infection. Children often undergo surgical repair of congenital conditions and are treated differently from adults with respect to the process of catheter insertion and care. Approximately 160,000 children are hospitalized in pediatric intensive care units (PICUs) annually in the US, Using a conservative estimate of a 5-15% incidence of nosocomial infections, between 8,000 and 24,000 children would acquire nosocomial infections annually. Based on studies of adult patients, these infections would result in 48,000 to 144,000 additional lCU days, between 56,000 and 168,000 additional hospital days, would cost between $320 and $960 million dollars and be responsible for 2,000 to 6,000 deaths annually. I propose to perform a series of studies of PICU patients over five years with the following specific aims: 1) To determine the morbidity, mortality, and excess costs attributable to nosocomial primary bloodstream infection in critically ill pediatric patients 2) To determine patterns of bacterial colonization in arterial and central venous catheters, specifically to correlate arterial and central venous catheter colonization in PICU patients over time with the risk of nosocomial primary bloodstream infection, controlling for severity of illness, and 3) To determine if implementing a standard protocol for arterial catheter insertion and care can decrease nosocomial bloodstream infection rates by 25% and to determine the cost-benefit of this intervention. My longterm career goal is to become an academic Pediatric Infectious Diseases specialist performing innovative patient-oriented research. My immediate goals are to learn epidemiologic and statistical methods in order to study the rates, risk factors and attributable outcomes of nosocomial infections in Pediatric Intensive Care Unit patients. I intend to achieve these goals by obtaining a Master's degree in Public Health with a concentration in epidemiology and performing patient-oriented research under the guidance of an experienced mentor and research advisory group. Specific studies of nosocomial infections in pediatric patients are needed to determine infection rates, risk factors that are unique to the processes of care in pediatrics, and outcomes attributable to nosocomial infections, in order to develop effective prevention interventions.